1. Field of the Invention
The invention relates to a blood pump, and more particularly, the invention relates to a centrifugal blood pump with a disposable pump element and a reusable motor element.
2. Brief Description of the Related Art
Blood pumps used in surgical procedures such as cardiopulmonary bypass (CPB) and coronary artery bypass grafting (CABG) are single-use devices. These blood pumps are generally powered by a reusable motor which drives the pump through a magnetic coupling. However, the reusable motors are not sterilizable. Thus, the motor and attached pump are positioned outside the sterile surgical field at a location away from the patient. The disposable pump which is driven by the motor is connected to the patient by long lengths of tubing which transport the patient's blood to and from the blood pump. The long lengths of tubing increase the priming volume of the pump which is the amount of the patient's blood and/or saline which must be drawn into the tubing and the pump to prime the pump before blood begins to be returned to the patient.
Long lengths of tubing connecting the pump to the patient also increase the amount of foreign material which comes into contact with the patient's blood, increasing trauma to the patient. A typical CPB circuit includes several feet of flexible tubing that the patient's blood flows through. In order to prevent blood clots, the patient's blood is generally treated with Heparin. The use of Heparin is preferably minimized because Heparin prevents the blood from clotting.
In addition to the priming volume problem with known blood pumps the magnetic coupling for transmitting rotation between the pump and the motor has associated disadvantages. With the magnetic coupling, accurate measurements of the load on the pump are difficult to obtain because of the possible slippage that occurs between the magnets of the magnetic coupling. Because the coupling is not direct, the magnetic plates may slip relative to each other resulting in the motor turning faster than the pump impeller. Further, the current drawn by the motor to control the rotation of the rotor, is used in these devices for measurement of impeller loads. Due to the possible slippage of the magnetic coupling between the pump impeller and motor unit an accurate measurement of current is difficult to obtain.
Previous attempts to move the blood pump closer to the patient have involved the use of a cable drive between the motor and the pump which allows the sterile pump to be located within the sterile surgical field while the motor is placed outside of the sterile surgical field. The use of a cable drive increases the load on the motor due to friction between the cable housing and the cable and makes it more difficult to accurately control the pumping volume due to rpm fluctuations. Also, the use of a cable introduces the possibility of the cable breaking or becoming kinked during the surgical procedure causing pump failure.
Blood pumps may be used during still heart surgery where the bypass pump is needed to perform the work of the heart. Alternatively, heart surgery may be done on a beating heart. During beating heart surgery the blood pump is used to provide supplemental support. In addition, during a beating heart surgical procedure the heart may fibrillate and cease pumping blood thereby requiring full support. Therefore it is necessary that the blood pump utilized for beating heart supplemental support be capable of providing full CPB support if needed. In either stopped heart or beating heart surgery, it is desirable to minimize the priming volume of the blood pump by placing the pump as close as possible to the surgical site. By placing the pump closer to the surgical field, the amount of saline required to prime the bypass circuit is reduced which reduces the likelihood that a transfusion will be required.
Accordingly, it would be desirable to provide a blood pump which can be positioned within the surgical field close to the surgical site to minimize the priming volume of the pump. In order to position the pump within the surgical field close to the heart, the pump and associated motor must be provided in a sterile condition.